It is known to electrically couple multiple DC-to-DC sub-converters in parallel to increase DC-to-DC converter capacity and/or to improve DC-to-DC converter performance. One type of DC-to-DC converter with multiple switching sub-converters is a “multi-phase” DC-to-DC converter, where the sub-converters, which are often referred to as “phases,” switch out-of-phase with respect to each other in at least some operating modes. Such out-of-phase switching results in ripple current cancellation at the converter output filter and allows the multi-phase DC-to-DC converter to have a better transient response than an otherwise similar single-phase DC-to-DC converter.
A multi-phase DC-to-DC converter's performance can be improved by magnetically coupling the energy storage inductors of two or more phases. Such magnetic coupling results in ripple current cancellation in the inductors and increases ripple switching frequency, thereby improving converter transient response, reducing input and output filtering requirements, and/or improving converter efficiency, relative to an otherwise identical converter without magnetically coupled inductors.
Two or more magnetically coupled inductors are often collectively referred to as a “coupled inductor” and have associated leakage inductance and magnetizing inductance values. Magnetizing inductance is associated with magnetic coupling between windings; thus, the larger the magnetizing inductance, the stronger the magnetic coupling between windings. Leakage inductance, on the other hand, is associated with energy storage. Thus, the larger the leakage inductance, the more energy stored in the inductor. Leakage inductance results from leakage magnetic flux, which is magnetic flux generated by current flowing through one winding of the coupled inductor that is not coupled to the other windings of the inductor.
A DC-to-DC converter including one or more inductors may operate in a continuous conduction mode (CCM) or in a discontinuous conduction mode (DCM). CCM is characterized by current through the one or more inductors continuously flowing, such that the current is always greater than zero. DCM, in contrast, is characterized by current through the one or more inductors remaining at zero for a portion of each switching period. CCM promotes fast transient response and high heavy-load efficiency. Consequently, DC-to-DC converters are commonly designed to operate in CCM at heavy loads. However, CCM can be relatively inefficient at light loads. Therefore, many DC-to-DC converters are designed operate in DCM under light loads.